Active management is required to regenerate the Caledonian forest: Alladale as a case study

Passive approaches to nature recovery have been hailed as a low-cost approach to boosting biodiversity in ecologically degraded sites. But there remains little evidence of whether this generalises to all climatic and ecological contexts. To address this knowledge gap, we used satellite remote sensing to examine vegetation change in Alladale Wilderness Reserve, a remote rewilding site in Scotland where active and passive approaches have simultaneously taken place for the past decades. In contrast to enclosures and tree planting, more passive approaches did not help regenerate the native Caledonian forest, failing to lead to structural or functional change within Alladale, relative to the wider landscape. Observed changes under both approaches were moreover much less dramatic than those reported for the Knepp Estate, another established rewilding site in Southern England. Our results suggest that passive rewilding is unlikely to promote significant biodiversity change in areas where recent human forcing of ecological processes has been limited, even if past human pressures have intensively reshaped the ecosystem-as seen in Alladale. In such situations, active interventions are likely to be required to shift the system onto a new ecological trajectory. Altogether, our study illustrates how freely available satellite data can (1) help contrast the impacts of environmental management approaches on ecosystem structure and functioning, in ways that complement existing ground-based studies; and (2) help distinguish areas likely to benefit from passive nature recovery approaches from those where specific active interventions are needed. We use long-term satellite data to test the efficacy of passive and active approaches to nature recovery in Alladale Wilderness Reserve, in the Scottish Highlands. In contrast to enclosures and tree planting more passive approaches did not help regenerate the native Caledonian forest, failing to lead to structural or functional change within Alladale relative to the wider landscape. Our results suggest that passive rewilding is unlikely to promote significant biodiversity change in areas where recent human forcing of ecological processes has been limited, even if past human pressures have intensively reshaped the ecosystem-as seen in Alladale.image